1. Field of the Invention
The present invention relates to downhole packers. More particularly, the present invention relates to a two-stage, retrievable, expandable packer for sealing an annulus within a wellbore.
2. Background of the Related Art
Downhole packers are typically used to seal an annular area formed between two coaxially disposed tubulars within a wellbore. A packer may seal, for example, an annulus formed between production tubing disposed within wellbore casing. Alternatively, some packers seal an annulus between the outside of a tubular and an unlined borehole. Routine uses of packers include the protection of casing from pressure, both well and stimulation pressures, and protection of the wellbore casing from corrosive fluids. Other common uses may include the isolation of formations or of leaks within wellbore casing, squeezed perforation, or multiple producing zones of a well, thereby preventing migration of fluid or pressure between zones. Packers may also be used to hold kill fluids or treating fluids in the casing annulus.
Packers typically are either permanently set in a wellbore or retrievable. Permanent packers are installed in the wellbore with mechanical compression setting tools, fluid pressure devices, inflatable charges, or with cement or other materials pumped into an inflatable seal element. Due to the difficulty of removing permanent packers, retrievable packers to permit the deployment and retrieval of the packer from a particular wellbore location. Retrievable packers have a means for setting and then deactivating a sealing element, thereby permitting the device to be pulled back out of the wellbore.
Conventional packers typically comprise a sealing element between upper and lower retaining rings or elements. The sealing element is compressed to radially expand the sealing element outwardly into contact with the well casing therearound, thereby sealing the annulus.
One problem associated with conventional packers arises when a relatively large annular area between two tubulars is to be sealed. Conventional packers, because they rely solely on compressive forces applied to the ends of the sealing member, are sometimes ineffective in sealing these larger areas. If the annular area to be sealed is relatively large, the sealing element must be extensively compressed to fill the annulus. Often times, the element buckles due to the compressive forces, thereby effecting an incomplete seal or a seal that is prone to premature failure. Therefore, there is a need for an expandable packer that can be more effectively used in sealing annular areas between tubulars.
A packer for sealing an annulus in a wellbore is provided wherein the sealing element is actuated in a two-stage process. In one aspect, the packer comprises a body having a sealing element, a shoulder disposed there-around, and a slideable member arranged on the body. The slideable member has a first surface disposable beneath the element to increase the inner diameter thereof and a second surface disposable against an end of the element to compress the element against the shoulder to increase the outer diameter thereof.
In another aspect, the invention comprises a packer for sealing an annulus in a wellbore, comprising an annular body having at least one port disposed in an outer surface thereof; a shoulder disposed about the body; a slideable member slideably disposed about the body; and a sealing element disposed about the body between the shoulder and the slideable member whereby the element is expandable upon movement of the slideable member towards the shoulder. The slideable member has a first surface disposable beneath the element to increase the inner diameter thereof and a second surface disposable against an end of the element to compress the element and increase the outer diameter thereof. The ratchet mechanism retains the element in the compressed position to seal an annular area between the body and the inner surface of the tubular.
In still another aspect, a method for actuating a packer in a wellbore is provided. The method comprises running a body into the wellbore, the body comprising a sealing element a shoulder, and a slideable member slideably disposed there-around, wherein the slideable member comprise a first surface and a second surface; forcing the first surface beneath the element to increase the inner diameter thereof; and forcing the second surface against an end of the element to increase the outer diameter thereof.